1. Field of the Invention
The present invention relates to a method of deforming an initial pipe having a circular cross-section into an U-shaped section and to a device for carrying out the method.
2. Description of the Related Art
U-shaped sections produced by a chipless deforming process from circular initial pipes are used, for example, as suspension or control arms for the rear axles of automobiles.
In the deforming process which has been carried out in the past, an initial pipe is placed on the edges of an open bottom die which has an internal contour corresponding to the external contour of the U-shaped section. The opening dimension of the opening of the die is always smaller than the diameter of the initial pipe. Using a ledge-like top die, which has a convexly curved front portion, the initial pipe is pressed in from the side located opposite the bottom die. The top die has an external contour which corresponds to the internal contour of the section.
In view of the fact that the opening dimension of the bottom die is always smaller than the diameter of the initial pipe, it was necessary in the past during the deformation of the initial pipe to pull generally about a third of the pipe diameter over the edges of the bottom die. This results immediately in front of the end position of the top die in a situation for so-called ear loops in such a way that, due to the section modulus occurring at the ear loops, the material located at the bottom is stretched or elongated at the inner side thereof. This elongation is particularly due to the fact that, by moving the top and bottom dies toward each other, the material in the gap available on both sides between the top die and the bottom die is prevented from carrying out a sliding and rolling movement by the high friction at the walls of the top die and the bottom die. This stretching or elongation always takes place transversely of the rolling direction of the metal from which the initial pipe is manufactured, so that the mechanical technological characteristics are significantly limited as compared to those in the longitudinal direction. Consequently, depending on the mechanical characteristics, the maximum plastic transverse elongation is in the border area of the actually occurring elongation values.
In the case of surface roughness, which may be relatively great particularly when using initial pipes manufactured from hot-rolled sheet metal, a critical tear situation may occur in the upper border range of the roughness values.